The present invention relates to an inverter device for controlling the operation of a three-phase motor.
In a hybrid or an electric vehicle, a motor for driving the vehicle or a compressor is driven by a high-voltage battery and a communication device such as an audio instrument, LIN (Local Interconnect Network) or CAN (Controller Area Network) is driven by a low-voltage battery. In this structure, signals are sent and received through a photocoupler between a CPU for controlling an inverter device for the motor and another CPU for controlling the communication device (refer to, e.g. Japanese Patent Application Publication 2004-336907).
A filter circuit including a coil and a capacitor is provided in input stage of the inverter device for controlling motor drive for suppressing the noise of output voltage of the inverter device. Since the capacitor is provided in the input stage of the inverter device, it takes time for the capacitor storing the electric power to be discharged when it is disconnected from the high-voltage battery and, accordingly, the voltage at the input stage will not decrease quickly. Therefore, when the voltage of the input stage is required to decrease within a predetermined length of time after disconnection from the high-voltage battery, the above structure may not satisfy such requirement.
To reduce the electric power stored in the capacitor in the input stage of the inverter device below a predetermined value in a predetermined length of time, some methods may be contemplated such as connecting a resistor in parallel with the capacitor or connecting a resistor to the capacitor in response to the detection of disconnection from the high-voltage battery. However, in the former case in which the resistor is always connected to the high-voltage battery, power is consumed by the resistor uselessly and the temperature is raised, accordingly. Therefore, the device should be enlarged or the generated heat should be released so that the temperature may not rise excessively. In the latter case, a circuit for detecting the disconnection from the high-voltage battery needs to be added.
To reduce the electric power of the capacitor in the input stage of the inverter device below a predetermined value in a predetermined length of time, the capacitance of the capacitor needs to be decreased, but the inverter device may not be driven properly when the capacitance of the capacitor is simply made small.
The present invention is directed to providing an inverter device that makes it possible for the capacitor in the input stage of the inverter to reduce the voltage at the input stage to a predetermined level within a predetermined length of time by reducing the capacitance of the capacitor, without using an additional circuit for releasing the electric power stored in the capacitor.